The Cell CycleGrowth, Duplication & Division

Eukaryotic Cell Cycle

• An orderly sequence of events in which a cell grows, duplicates its contents and then divides in two

Stages of the Cell Cycle

• Interphase

• Mitosis

• Cytokinesis

Interphase

• During interphase the cell grows, makes organelles and duplicates (copies) its DNA.

– G1: the cell grows, makes organelles and prepares for S-phase

– S-phase “synthesis phase” This is when DNA replication occurs, i.e. the cell copies its DNA

– G2 the cell grows, makes organelles and prepares for mitosis and cytokinesis

Mitosis:

• Division of the nucleus

• 4 Phases

– Prophase

– Metaphase

– Anaphase

– Telophase

DNA

• DNA can be found in one of two forms during the cell cycle: chromatin or chromosome.Both consist of DNA wrapped around proteins

– Chromatin is the relaxed or uncondensed form of DNA. In this state, DNA looks like thread or spaghetti

– A Chromosome forms when chromatin becomes highly condensed. In this state, DNA looks like a rod or an X (two rods)

Prophase

• Chromatin condenses into chromosomes

• The nuclear membrane breaks down

• Mitotic spindle begins to form between the poles

Metaphase

• Chromosomes attach to the mitotic spindle and line up along the equator of the cell

Anaphase

• Microtubules of the mitotic spindle shorten, pulling chromosomes to opposite ends of the cell

Telophase

• Nuclear envelope reforms

• Chromosomes decondense

• The mitotic spindle is disassembled

Cytokinesis

• Division of the cytoplasm (cytosol & organelles)

– In animal cells a cleavage furrow forms along the equator and pinches inward until the cell divides

In plant cells a cell plate forms between the two daughter nuclei and grows until it divides the cell.

The End Result:

• The cell cycle produces two daughter cells that are genetically identical to the parent cell

Dividing HeLa cells

Cell cycle regulation

1. a. Cyclins -Proteins that bind to receptor enzymes that

. initiate the next step.

. b. Checkpoints. .

2. Cancer (Rapid, uncontrolled growth of cells)

a. Cells spend less time in Interphase.

b. Carcinogens.

c. Tumors

d. Why doesn’t everyone get it?

- Benign vs. Malignant

- Metastasis

Note: Stem Cells